Question

I want to create unique directory for controlling directory’s disk quota. The unique directory name is created as follows:

unique_string()->
    base64:encode_to_string(term_to_binary(make_ref())).

But when debuging, the problem appears:

 exception exit: {{badmatch,
                         {error,
                             " g3IAA2QAFGVtYWNzQHl1cy1pTWFjLmxvY2FsAwAB/ncAAAA8AAAAAA==: No such file or directory.\r\n"}},

The unique_string contains “/”, it caused problems.

I am afraid if just deleting “/”, the feature of unique will lost. How to solve problem?
In addition, is there any other characters can’t be used in directory?

Answer 1

You can replace base64:encode_to_string with a hexify function as follows.

hexify(Binary) ->
  lists:flatten([io_lib:format("~2.16.0b", [B]) || <<B>> <= Binary]).

You can also tweak this function to allow different set of characters used.

btw, I recommend to do some hashing on the ref to make the names of same length.

hexify(crypto:md5(term_to_binary(make_ref())))